Welding apparatus



Feb. 15, 1944. w. A. WEIGHTMAN 2,342,094

WELDING APPARATUS Original Filed April 30, 1941 '7 Sheets-Sheet l N V E N TOR WLUiamHWeightmcm A TTORNE Y WELDING APPARATUS Original Filed April 50, l94l '7 Sheets-Sheet 2 PICIZ //\/l E/VTOP 3g WilliqmQWeighlmun A TTORNE Y Feb. 15, 1944.

w. A. WEIGHTMAN 2,342,094

WELDING APPARATUS Original Filed April 30, 1941 7 SheetsSheet 3 LL i lNl/ENTOR W UliamQWeig h t mun QVA M ATTORNEY N V E N TOR Wmghtmcm 7 Sheets-Sheet 4 w. A. WEIGHTMAN WELDING APPARATUS Original Filed April 50. 1941 Q m :E E: O 0

Feb. 15, 1944.

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Feb. 15, 1944. w. A. WEIGHTMAN WELDING APPARATUS Original Filed April 30, 1941 '7 Sheets-Sheet 5 /Nl ENTOR William QWeighrmcmU BY W 5: 7

A TTOPNEY W. A. WEIGHTMAN WELDING APPARATUS '7 Sheets-Sheet 6 INVENTOR WilliamwQ-Wmghhmn,

A TTORNEY Feb. 15, 1944.

,Original Filed April 50, 1941 Feb. 15, 1944. w WE|GHTMAN 2,342,094

WELDING APPARATUS Original Filed April 30, 1941 7 Sheets-Sheet 7 PIGB /NVENTOR W'LULQrQWeigh cmcm 7241 0? Patented Feb. 15, 1944 WELDING APPARATUS William A. Weightman, Philadelphia, Pa., assignor to Edward G. Budd Manufacturing Company, Philadelphia, Pa., a corporation of Pennsylvania Original application April 30, 1941, Serial No. 391,056. Divided and this application January 21, 1942, Serial No. 427,560

v 11 Claims.

This application is a'division of my copending application Serial No. 391,056, filed April 30, 1941. for Welding apparatus, now Patent No. 2,323,361, dated July 6, 1943.

This invention relates to electric spot welding apparatus, more particularly to spot welding ap; paratus of the traveling-electrode type for welding metal sheets of curvilinear contour.

One of the objects of the present invention is to provide welding apparatus of new and improved construction for spot welding sheets of metal of curvilinear contour with great dispatch and economy of operation. I

Another object is to provide improved spot welding apparatus of the traveling-electrode type in which the electrode is mounted on a carriage adapted to move along a curvilinear path of travel with new and improved means for propelling the carriage and for conducting electric current to the welding electrode.

Another object is to provide a traveling welder with an electrode-supporting carriage which is movable along a curved path of travel and adapted to automatically perform spot welding operations at regular intervals on a workpiece of curvilinear contour, and with a second carriage movable along a straight-line path of travel and adapted to drive the electrode-supporting carriage along its curvilinear path of travel, which second carriage also supports a transformer for supplying current to the electrode.

Another object is to provide a traveling spot welder having a pair of carriages, one supporting,

an electrode device and the other supporting driving mechanism for propelling both carriages along different paths of travel with a new and improved means for conducting welding current from a transformer mounted on one carriage to the electrode device supported by the other carriage.

A further obiect is to provide a spot welding electrode device of improved construction which is adapted to travel relative to a fixed workpiece and perform spot welding operations at regular intervals while the support therefor is traveling continuously in a predetermined path and in which the electrgde lags behind the support during each spot welding operation and returns thereafter to normal position for performing the next spot welding operation.

With the above and other objects in view, the present invention consists in certain features of construction and combinations of parts to be hereinafter described with reference to the accompanying drawings and then claimed.

In the drawings which illustrate a suitable embodiment of the invention:

Figure 1 is a side elevation of the spot welding apparatus, one of the side portions of the frame being removed to more clearly show the various part of the welding apparatus;

Figure 2 is a vertical section taken approximately on the line 2-2 of Figure 1;

Figure 3 is a top plan view of the apparatus shown in Figure 1, portions of the housings for the driving mechanism being removed to show the driving mechanism in greater detail;

Figure 4 is a transverse section taken approximately on the line 4-4 of Figure 1, looking downwardly upon the carriage upon which the welding electrodes are mounted; I

Figure 5 is a longitudinal section taken approximately on the line 5-5 of Figure 3;

Figure 6 is a section taken approximately on the line 6-6 of Figure 4;

Figure '7 is an enlarged sectional view through one of the electrode devices showing the mechanism for operating the same;

Figure 8 is a section similar to Figure 7, showing the electrode device in operative position for welding the work-piece.

Referring to the accompanying drawings, in which like numerals refer to like parts throughout the several views, the welding apparatus il- 1ustrated is especially adapted for electrically spot welding sheets of metal of curvilinear contour, although the improved electrode device associated therewith is suitable for welding sheets of metal in the flat.

The articles A selected for illustrations are corrugated strips of sheet metal of curvilinear contour having a sharp curvature at opposed regions, as shown in Figures 1 and 2, which are supported in arch-like arrangement on a correspondingly shaped stationary jig J (to be later described in detail) with the adjacent portions to be welded together in overlapping engage- -m ".nt as indicated at 30 in Figure 2 In the welding apparatus of the present invention, the work remains stationary and the welding electrode or electrodes, as the case may be, move relative to the work and are so arranged as to start the welding operation at one end of the work and travel at a uniform rate in a curvilinear path of travel and spot weld the overlapping edges'of the work A at regularly spaced. intervals.

In general, the welding apparatus embodies a frame F recessed at its bottom side to bridge the article A as shown in Figure 1, a lower carriage C--l supporting a pair of electrode device E and being supported by the frame F for -movement in a curvilinear path corresponding to means, tobe later described, for propelling both carriages and a transformer for supplying electric current to the electrodes.

The jig J The jig J as shown in Figures 1, 2 and 8, selected for illustration,- embodies a bed 20 comprised of suitable rigid framing which supports a plurality of rigid arched members 22 having their ends secured to the bed 20. The members 22 are arched in shape to conform to the contour of the sheets of metal A and are secured together by bolts 24 to provide spaced recesses 26, as shown in Figure 2, extending from one end thereof to the other.

Supported Within the recesses 26 are suitable electrode elements 28 having the exact curvilinear contour of the sheets A. Each electrode element 28 extendsfrom end to end of its recess 26. Referring to Figure 2, it will be noted that each electrode element 28 supports the overlapping edges 30 of adjacent sheets A and that the intermediate portion of each sheet A is supported on plates 32 secured to the elements 22, each plate 32 being spaced slightly as shown at 34 in Figure 2 from the adjoining electrode element 28.

The electrode elements 28 are grouped in pairs, the elements of each pair being insulated from the members 22, as at 36, and electrically connected by a conductor bar 38.

The plate elements 32 are provided at spaced intervals with protuberances 40 conforming in cross-section to the shape of the corrugation of the sheet to nest within the corrugations and hold the sheets in proper position during the welding operation. Preferably the ends of the sheets A are secured to the plates 32 by means of suitable clamps 42 and 44 as shown in Figure 1, which tend to pull the arch-like sheets A into firm engagement with the electrode elements 28 and plates 32.

The frame F The frame F as shown in Figures 1, 2 and 4 The lower carriage C- -"1 The lower carriage is best illustrated in Fig- I ures 1, 2, 4, 5 and 8. It embodies a frame or support I6 having a shaft I8 at one end, to the ends of which pinions 80 and guide rolls 82 are secured. The guide rolls 82 fit closely within the channel tracks 66 and the pinions 80 mesh with the racks 68 as shown in Figure 2. The opposite end of the support I6 is provided with axially aligned stub shafts I9 having rolls 83 thereon which engage with and ride in the channel tracks 66. Referring to Figure 5, it will be seen that the support I6 includes a fixed housing 84 surrounding a worm gear 86 secured to the shaft 18 and supporting a worm 88 in mesh with the gear 86. The pinion 88 is held against axial movement and the axis thereof is disposed in a vertical plane. v A suitable shaft 90 is secured to the pinion 88 coaxial therewith and extends forwardly therefrom for connection with the upper carriage C-2 in a manner to be presently described.

Suitably secured to the support I6 are bracket or secondary supports 92 having guideways 94 disposed perpendicular to a plane passing through the axes of the shaft I8 and stub shafts embodies spaced upright members 46 interconnected at their ends as shown in Figure 1 by cross members 48. The members 46 are recessed upwardly from their lower sides to provide an arch 50. Each leg of the arch is provided with spaced wheels 52 disposed to ride upon tracks or rails 54 arranged at the sides of the jig J. The frame F is movable along the rails 54 parallel to the jig J and the work A and may be provided with a propelling mechanism comprising racks 56 secured to the rails 54, and pinions 58 meshed with the racks 56. The pin ions 58 may be rotatedthrough shafts 60 and suitable gearing 62 by means of hand wheels 64 located at the ends of the frame as shown in Figure 1.

The upright members 46 are provided with channel-shaped guide tracks 66, the channels of which face each other as shown in Figure 2. Racks 68 are disposed adjacent the tracks 66, the tracks 66 and racks 68 corresponding in curvilinear contour with the work sheets A. It

I9. Engaged with each way 94 of each bracket support 92 through gibs 95 for sliding movement therein is a bracket 96. Each bracket 96 is reciprocated within its way 94 by means of a linkage mechanism shown in Figures? and 8, which comprises a bell-crank lever 98 pivoted by means of a pivot pin I00 to the bracket support 92 and a link I 02 pivoted at one end at I04 to one arm of the bell-crank lever 98 and at its other end to a pin I06 carried by the bracket 96. An air cylinder I68 is pivoted to the support 92 by means of a pivot pin H0. The cylinder is provided with a piston I I2 having a shaft I I4 which is pivoted by means of a'pin I I5 to the other arm of the bell-crank lever as shown in Figure 7. Air conduits H6 and H8 are provided at the opposite ends of the cylinder I08. for the flow of air into and out of the cylinder at opposite sides of the piston II2.

The retracted position of the bracket 96 is shown in Figure 7 and the extended position is shown in Figure 8. The extended position of the bracket 96 is predetermined by a stop I20 with which the link I02 engages, as shown in Figure 8, in which position it is to be noted that the axis of the pin I04 coincides with a line passing through the axes of the pins I00 and I06, as shown by the broken line I01 in Figure 8. As a result of this, pivotal movement of the bell-crank lever cannot be effected by forces exerted on the bracket 96 which ordinarily would tend to move the bracket to its retracted position. It is obvious that the bracket 96 can be retracted only by the admission of air into the cylinder I08 through the air conduit connection 8 to move the piston II2 to the left, as viewed in Figure 8.

Two electrode'devices E are provided, as seen in Figure 2. Each electrode device embodies a support I22 pivoted by means of a pin I24 extending between the sides of the bracket 86 as shown in Figures 4 and 8. The support I22 is provided with a tubular extension I26 which is surrounded by a circumferentially spaced tube I28. A suitable piston I30 is secured to the outermost ends of the extension I28 and the tube I20..

The piston I30 is housed within a cylinder I32, one end of which forms the support for an electrode I34 which is insulated, as shown at I36, from the end of thecylinder I32, as shown-in Figure 8.

The tubular passage I 38 of the extension I26 opens at one end into the space between the end of the cylinder I32 and the piston I30 and communicates at the other end with a passage I40 formed in the support I22, which, in turn, communlcates with a suitable air conduit I42. The annular space I44 between the extension I26 and the tube I28 communicates at one end through an aperture I46 with the space between the piston I30 and the other end of the cylinder I32, and communicates at its opposite end through an aperture I48 with a passage I50 in the support I22, which, in turn, communicates with an air conduit I52. By admitting air under pressure through conduit I42, for example, such air will cause the cylinder I32 to move axially of the piston I30 toward the lwork A, as shown in Figure 8, and by introducing air under pressure through conduit I52 such pressure upon release of the air in conduit I42 will cause the cylinder with a source of electrical energy.

I32 to axially retract to the position shown in Figure '1.

Each of the cylinders I32 is resiliently maintained in a normal position by means of a rod member 2I2 pivoted thereto by means of a pivot pin 2I4, the rod member 2I2 being slidable within a stub shaft 2I8, Coiled compression'springs 2 l8 are provided at opposite sides of the stub shaft 2 I6 and surround the member 2I2, suitable abutments 220 being provided for the ends of the springs 2I0. The springs 2I8 obviously by reason of the slidable mounting of the rod member 2I2 tend to resiliently maintain the cylinder I32 in a normal position and will return the cylinder to the normal position from a pivoted position.

The upper carriage C2 I66 is provided with a worm pinion I60 which drives a worm gear I10 mounted on a horizontal shaft I12. The shaft I12 carries pinions I14 which mesh with the racks 14 whereby to propel the carriage C2 along the frame portions 46.

A power take-off shaft I16 is provided at another point of the gear'train I62, which shaft is journ-alled in a bearing I18 mounted at one side of the carriage platform I54. The bearing I18 is axially aligned with a cylindrical member I80 mounted at the opposite side of the carriage platform I54. The bearing I18 and I80 pivotally support a housing I82 the member as shown in 1 the end of its travel in either direction.

Figure 3. The housing I82 is provided with axially aligned bearings I83 which support a tu-.

bular shaft I84. The shaft I84 is provided with a bevel gear I86 fixed thereto which meshes with a bevel pinion I88 secured to the take-off shaft I16 so that upon operation of the gear train I62 thepinion I88 is caused to rotate the gear I86 and the shaft I84. The passage through the tubular shaft I84 is square and slidably receives the upwardly extending shaft 00 of the lower carriage CI, which latter shaft is correspondingly shaped in cross-section so that it, in turn, is rotated by the shaft I84 to rotate the worm pinion and thereby propel the lower carriage The platform' I54 also supports a transformer I90 connected in a suitable manner (not shown) One pole of the secondary of the transformer is connected through a conductor I92 to one end of a bus bar I94 pivoted to a link I86 by means of a pivot pin I98, which link is, in turn, pivoted at I83 to the a platform I54,

The other end of the bus bar I04, as shown in Figures 4 and 5, is pivoted by means of pivot pin 200 to a second bus bar 202, a coiled spring 204 being employed to resiliently hold the ends of the bus bars together in good electrical con-. tact. The other end of the bus bar 202 is pivoted by means of a pin 206 to the carriage C2 as shown in Figure 4, a. coiled compression spring 208 being employed to insure a firm yet resilient electrical contact. A flexible conductor 2I0 connects the carriage frame with the electrode I34.

Each electrode I34 is connected in this manner with the secondary of the transformer so that the current flow is from one pole ofthe transformer through the pivoted bus bars I94, and 202, through the metal A to be welded and the one electrode element 28 is connected with the last-mentioned pole of the transformer secondary.

Suitable means are provided for controlling the supply of air under pressure to the cylinders I08 and I32 and also for timing the flow of current to the transformer I90. The cylinder air supply and the current supply are timed with respect to each other in order that'each welding operation is performed at timed intervals properly correlated with the supply of air to the electrode-actuating cylinders. In Figure 3 the numerals 222 and 224 indicate air control and current control timers respectively, which are actuated by cam elements 226 driven through suitable gearing 228 from the power take-off shaft I63.

The connections between the 'air supply conduits H6, H8, I42 and I52 and the air control timer 222 have not been shown, but it is to be understood that the timer 222 may be of any suitable construction and may be connected in a suitable manner with such conduits. Likewise, the electrical connections between the transformer and current timer have not been shown.

Suitable limit switches 230 may be provided on the upper carriage C2 for cutting off-the supply of current when the carriage C2 reaches outline at the left in Figure 1.

located at the right end of the frame andit can be seen that the carriage G-I is at its maximum distance from the carriage -2, in which position the driving connection through the shafts 93 and I84 is extended and the bus bars I94 and 202 are pivoted to an extended position. The brackets 96 which support the welding electrodes originally are retracted and in the position shown vin Figure 7. Before the welding operation is started, air under pressure is admitted through the conduits II6 into the cylinders I08 which causes the pistons II2 to move to the right, as viewed in Figure 7, to actuate the bell-crank levers 98 and links I02, which moves the brackets 96 to the extended position shown in Figure 8. This brings the electrodes I34 in close proximity to the sheets A. The apparatus thus is in position for performing the welding operation. The carriage C-I during the welding operation moves from the position shown in broken outline at the right of Figure 1 to the position shown in broken The carriage 0-2 likewise moves from the right end of the frame to the left end of the frame. .The spot welding of the two overlapping sheets A occurs at regular intervals throughout the travel of the lower carriage and is brought about by the timer devices 222 and 224. The carriage CTI moves continuously at a uniform rate of speed and drives the carriage 0-2 at a uniform speed. At each interval corresponding to the desired spacing of the spot welds air is admitted under pressure, under the control of the timer 222, through the conduits I42, which air flows through the passages I40 and the tubular extensions I62 into the spaces between the pistons I30 and the closed end of the cylinders I32 to move the cylinders axially away from the pistons to createthe desired pressure on the overlapping sheets A between the electrode elements 28 and the electrodes I34, the flow of current being timed to perform the welding operation upon the creation of the pressure upon the overlapping sheets A in the manner just described. The carriage C-I, of course, is traveling continuously from the right to the left, as viewed in Figure 8, and due to the pressure engagement of the'electrodes I34 with the sheets A, the electrodes I34, the cylinders I32 and the supports I22 pivot as unitary structures about the pivot pins I24 with the result .that the electrode devices lag behind the movement of the carriage C- -I and thus compress the springs 2I8. This lag is substantially momentary and only suflicient to permit the proper spot welding operation. At the properly timedv interval the flow of air through conduits I42 is released and fiowis produced through the conduits I52, which air under pressure acts between the pistons I30 and the packing end of the cylinders I32 to retract the pistons and electrodes I34, at which time springs 218 return the cylinders I32 from their pivoted positions to their normal positions ready for the next cycle of operation. This cycle of operation is repeated throughout the entire travel of the carriage C-I from one end to the other of the work being welded.

When the welding operation along the two seems is completed the air under pressure flowing through the conduits H6 is released and air under pressure is admitted through the conduits II8 which restores the pistons II2 to a position at the left of the cylinders, as viewed in Figure 8, and retracts the brackets 96 to move the electrode devices back to the position indicated in Figure 7. This movement is sufiicient for the electrodes I34 to clear the corrugations of the work being welded.

The operator, if additional seams are to be welded, then rotates one of the hand wheels 64 which through the shafts G0, the gears 62 and the pinion 58 and rack 56 moves the entire welding apparatus longitudinally of the work to position the welding electrodes above another pair of seams. The piston II2 is=again caused to move to the position shown in Figure 8 to condition the apparatus for the spot welding of the second pair of seams and during this welding operation the carriages move from the left to the right end of the frame F.

It is seen from the foregoing description that novel means is provided for actuating an'electrode-supporting carriage for welding sheet metal articles of curvilinear contour, especially articles of relatively sharp curvature. The welding operation is automatic, and by providing the continuous moving carriage the welding operation is performed rapidly and uniformly. Another important feature uf the present invention is that the means for driving the electrode-supporting carriage is eflicient in itsoperation and eliminates the use of trailing cables and conduits adjacent the welding electrode. The particular construction described also further permits the welding transformer to be carried by the mechanism which operates the electrode-supporting carriage.

The electrode device itself, that is, the entire carriage C-I, is also equally as adaptable for use in welding flat sheets of metal as the welding of sheets of curvilinear contour.

While two electrodes have been shown connected in series, it is to be understood that only in quantity production as no time is lost by the need of returning the welded electrodes to an initial starting position.

Though only a single form of the invention is illustrated and described the invention is not limited thereto but may be embodied in various forms as desired. As various changes in con- ,'struction and arrangement of parts may be made without separating from the spirit of the invention as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In a traveling welder having a fixed electrode upon which the work to be welded is supported in fixed relation, a carriage movable in a predetermined'path of travel relative to said electrode, an electrode support pivoted to said carriage, a reciprocable electrode holder carried by said support, a second electrode carried by.

" said holder, an element pivotally carried by said carriage, a secondelement pivoted to said electrode holder and having a slidable connection with said first element, spring means associated with said elements for maintaining said holder resiliently and positively in a normal pressure position radial to the center of curvature of movement of said carriage and for returning said holder from a displaced pivoted position to said normal position, and means for reciprocating said holder to move said second electrode into and out of engagement with the workpiece.

2. In a traveling welder having a fixed electrode upon which the work to be welded is supported in fixed relation, a carriage movable in a predetermined path of travel relative to said electrode, a second electrode, a reciprocable holder for said second electrode, bracket means, means pivotally mounting said holder on said bracket means, means mounting said bracket means on said carriage for movement toward and away from the workpiece, fluid-pressure means for moving said bracket means, and fluid-pressure means for reciprocating said electrode holder.

3. In a traveling welder having a fixed electrode upon which the work to be welded is supported in fixed relation, a carriage movable in a predetermined path of travel relative to said electrode, a second electrode, a reciprocable holder for said second electrode, bracket means, means pivotallym'ounting said holder on said bracket means, means mounting said bracket means on said carriage for movement toward and away from the workpiece, fluid-pressure means for moving said bracket means, including means for locking said bracket means in one of its positions against movement other than by said fluidpressure means, and fluid-pressure means for reciprocating said electrode holder.

4. In a traveling welder having a fixed electrode upon which the work to bewelded is supported in fixed relation, a carriage movable in a predetermined path of travel relative to said electrode, a second electrode, a reciprocable holder for said second electrode for pressure engaging said electrode with the workpiece, bracket means 'pivotally supporting said holder, said bracket means being reciprocably mounted on said carriage for movement toward and away from the workpiece, fluid-pressure means for reciprocating said bracket means to position said second electrode adjacent the workpiece, and fluid-pressure means for subsequently reciprocating said electrode holder to force said electrode into pressure engagement with the workpiece.

5. In a traveling welder having a fixed electrode upon which the work to be welded is supported in fixed relation, a carriage movable in a predetermined path of travel relative to said electrode, a bracket support on said carriage, a

bracket slidably mounted on said support for movement from a retracted to an extended position and vice versa, a bell-crank lever pivoted to said bracket support, a link pivoted to said bracket and to one arm of said lever, a fluidpressure cylinder pivoted to said support and having a piston reciprocable therein, a piston rod secured to said piston and pivoted to the other arm of said lever, the pivot axes of said link and bell-crank lever being disposable in a common plane in the extended position of said bracket, and a second welding electrode supported on said bracket.

6. In a traveling welder having a fixed electrode upon which the work to be welded is supported in fixed relation, a carriage movable in a predetermined path of travel relative to said electrode, a bracket support on said carriage, a bracket slidably mounted on said support for movement from a retracted to an extended position and vice versa, a bell-crank lever pivoted to said bracket support, a link pivoted to said bracket and to one arm of said lever, a fluid-pressure cylinder pivoted to said support and having a piston reciprocable therein, a piston rod secured to said piston and pivoted to the other arm of said lever, the pivot axes of said link and bell-crank lever being disposable in a common plane in the extended position of said bracket, and a second welding electrode supported on said bracket, said second electrode including a support pivoted to said bracket, and a fluid-pressure cylinder and piston interposed between said support and second electrode for reciprocating said second electrode relative to said bracket.

7. In a traveling welder having a fixed electrode upon which the work to be welded is supported in fixed relation, a carriage movable in a. predetermined path of travel relative to said electrode, a bracket support on said carriage, a bracket slidably mounted on said support for movement from a retracted to an extended position and vice versa, a bell-crank lever pivoted to said bracket support, a link pivoted to said bracket and to one arm of said lever, a fluidpressure cylinder pivoted to said support and having a piston reciprocable therein, a piston rod secured to said piston and pivoted to the other.

arm of said lever, the pivot axes of said link and bell-crank lever being disposable in a common plane in the extended position of said bracket,

and a second welding electrode supported on said bracket, said second electrode including a support pivoted to said bracket, and a fluid-pressure cylinder and piston interposed between said support and second electrode for reciprocating said second electrode relative to said bracket, and resilient means urging said support, cylinder, piston and electrode as a unit to a normal predetermined position.

8. In a welder having an electrode upon which the work to be welded is supported, a second electrode, a movable holder for said second electrode,

a secondary support, means mounting said holder on said secondary support for bodily movement relative thereto, a primary support, means mounting said secondary support on said primary support for movement toward and away from said primary support and first electrode, means for moving said secondary support, and means for moving said electrode holder.

9. In a welder having an electrode upon which the work to be welded is supported, a second electrode, a reciprocable holder for said second.

electrode, a secondary support, means mounting said holder on said secondary support for pivotal movement relative thereto, a primary support, means mounting said secondary support on said primary support for movement toward and away from said primary support and first electrode, means for reciprocating said secondary support and means for reciprocating said electrode holder.

10. In a traveling welder having a fixed electrode upon which the work to be welded is supported in fixed relation and a carriage movable n a predetermined path of travel relative to said electrode, an electrode support movably mounted on said carriage, a reciprocable electrode holder carried by said support, a second electrode carried by said holder, single means for reciprocating said holder and establishing workpiece pressure between said electrodes and resilient and positive means for maintaining said holder in a position substantially radial to curvature of movement of said carriage irrespective of the reciprocation of the holder on said support.

11. In a traveling welder having a fixed electrode upon which the work to be welded is supported in fixed relation and a carriage movable in a predetermined path of travel relative to said electrode, an electrode support movably mounted 15 on said carriage, a reciprocable electrode holder carried by said support, a second electrode carried by said holder, single means for reciprocating said holder and establishing workpiece pressure between said electrodes and resilient and positive 

